1. Field of the Invention
The present invention relates to the structure of a stereoviewer for viewing a pair of stereoscopic photographs three-dimensionally through binocular lenses.
2. Description of the Prior Art
A stereoviewer is an apparatus for viewing a subject three-dimensionally by viewing through binocular lenses a pair of photographs of the same subject which are taken from rightward and leftward points. Such a stereo pair of photographs are taken by a stereoscopic camera equipped with two photographing lenses or by one camera and from rightward and leftward points.
FIG. 8(A) is an external view of a stereoscopic camera. The stereoscopic camera is composed of a main body 1 provided with a finder 2 and a shutter button 3, and two matched photographing lenses 4, 5 provided on the front surface of the main body 1 with an interval of about 70 mm between the two lenses 4, 5. A subject to be taken is positioned through the finder 2 and taken on the film mounted on the main body 5 through the photographing lenses 4, 5 by pressing the shutter button 3. Two images caught from different angles are thus projected on the film.
FIG. 8(B) shows the structure of a conventional simple stereoviewer. A stereo pairs of photographs 7 (hereinunder referred to as "stereoscopic photographs") printed on photographic paper from the film is inserted into a photograph holder 6A. The stereoscopic viewer is provided with binocular lenses 8A, 8B so as to view the stereoscopic photographs 7 therethrough at a least distance (about 25 cm) of distinct vision. By viewing the stereoscopic photographs 7 through the binocular lenses 8A, 8B, it is possible to view the images as a three-dimensional image.
Since the conventional stereoviewer shown in FIG. 8(B) is handled separately from the stereoscopic camera shown in FIG. 8(A), the user cannot view a three-dimensional image immediately after he receives the images printed on photographic paper as the stereoscopic photographs 7, and the user finds it a bother to view the stereoscopic photographs 7 through a stereoviewer. In addition, since the stereoviewer is manufactured separately from the stereoscopic camera, the manufacturing cost separate from that of the stereoscopic camera is charged against the user to his disadvantage.
In the conventional stereoviewer, a convex lens having a constant curvature is used for the binocular lenses 8A, 8B. It is therefore not possible for people of all ages to adjust the focal length of the binocular lenses 8A, 8B. That is, when a person grows old, he becomes farsighted and the image of a substance is formed behind the retina. It is therefore difficult to view the stereoscopic photographs at a least distance of distinct view through the ordinary binocular lenses 8.
When the stereo pair of photographs shown in FIG. 8(B), which are arranged with a predetermined space therebetween, are observed through the binocular lenses 8, the observer recognizes the images on the stereoscopic photographs as a three-dimensional image by superimposing the stereo pair of photographs 7 on each other with the observer's eyes. It is, however, difficult for an observer having the eyes at a narrow distance from each other to superimpose the stereoscopic photographs 7.